This invention relates to a method for detecting an incorrect installation of lambda probes in an internal-combustion engine with two cylinder banks, each having its own exhaust gas catalyst which has a lambda probe with a lambda control unit connected thereto, and whose injection valves can be switched off at least by cylinder bank.
German Patent Application P 43 34 557.3, which has not yet been published, discloses an arrangement for idling control of a motor vehicle internal-combustion engine with two cylinder banks to which one exhaust gas catalyst respectively is assigned which comprises a lambda probe. In this known device, the injection valves of one of the two cylinder banks are alternately switched off during the idling operation of the internal-combustion engine. The switching off of the injection valves of an internal-combustion engine by cylinder banks is therefore known from the above-mentioned document.
In internal-combustion engine controls with two separate lambda control circuits, there is the risk that the lambda probes of the exhaust gas catalysts, which are interchangeable, and are provided separately for the two cylinder banks, may be installed improperly with the left hand probe being connected on the right and vice, versa. (That is, two are reversed or interchanged.) This has the effect that one cylinder bank of the internal-combustion engine becomes too lean and the other becomes too rich, up to the maximal control limit of the lambda control. As a result, the internal-combustion engine runs erratically, significantly reducing comfort.
So that the lambda probes can no longer be improperly interchanged in this manner, they could be mechanically coded, for example by different plug-type connections or by different cable lengths for the left and for the right lambda probe. However, this approach would violate the principle of identical parts for the lambda probes, which would increase their costs.
It is therefore an object of the invention to provide a simple and cost-effective method for recognizing lambda probes which are improperly connected, or interchanged, in this manner, in the case of an internal-combustion engine with two cylinder banks to which separate exhaust gas catalysts are assigned which have a lambda probe and a lambda control unit connected thereto.
This object is achieved according to the invention, in that the injection valves of one of the two cylinder banks are switched off for a time which corresponds at least to the reaction or change-over time of the lambda probes. The lambda probe signal of the lambda probe assigned to the switched-off cylinder bank is then compared (at the end of the switch-off time of the injection valves) with a predetermined threshold value, and an interchanged connection of the lambda probes is determined to exist when the lambda probe signal exceeds or falls below the threshold value. The threshold value will be exceeded when the lambda probe emits a small signal in the case of a lean mixture and a large signal in the case of a rich mixture. Analogously, the signal will fall below the threshold value when the lambda probe emits a large signal in the case of a lean mixture and a small signal in the case of a rich mixture.
In an advantageous embodiment of the method according to the invention, the lambda controls are blocked and an error indication device is activated when an interchanged connection of the lambda probes is recognized.
In a further embodiment of the method according to the invention, an external testing device which can be connected to a diagnostic connection of the internal-combustion engine is used to recognize an interchanged connection of the lambda probes.
Advantageously, the method according to the invention can also be included in the internal-combustion engine control devices as a so-called on-board diagnostic function. As a result, an improper exchange of the lambda probes would be recognized immediately also between visits to the repair shop.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.